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how to subscribe to usb_cam/image_raw to process the image from camera?

asked 2016-12-26 01:33:34 -0500

chaiein gravatar image

updated 2016-12-26 09:22:17 -0500

gvdhoorn gravatar image

what is missing in the below code that is used for subscribing to the topic /usb_cam/image_raw.

void chatterCallback(const std_msgs::String::ConstPtr& msg)
  ROS_INFO("I heard: [%s]", msg->data.c_str());

int main(int argc, char **argv)
  ros::init(argc, argv, "main");
  ros::NodeHandle n;

  std::cout<<"Subscribing starts!"<<std::endl;
  ros::Subscriber sub = n.subscribe("usb_cam/image_raw", 2, chatterCallback);

  return 0;

how to get the image from the camera so that i need to process this image. Is there any files missing in the header.

~/usb_cam/launch$ rostopic info /usb_cam/image_raw
Type: std_msgs/String

Publishers: None

 * /listener (http://ubuntu:42711/)
 * /main (http://ubuntu:35605/)
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answered 2016-12-26 12:38:29 -0500

NEngelhard gravatar image

image_raw is most probably a sensor_msgs/Image and not a std_msgs/String so you will need to change the callback function to expect this data type.

So rather

void chatterCallback(const sensor_msgs::Image::ConstPtr& msg)
  ROS_INFO("Received image with size: %i x %i", msg->width, msg->height);
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Asked: 2016-12-26 01:33:34 -0500

Seen: 973 times

Last updated: Dec 26 '16